68 SOME MINUTE ANIMAL PARASITES 



and several methods of examination have been 

 adopted, with invariably the same results. 



The nucleus of a spirochsete is of a complicated 

 nature. First, the body of the organism is traversed 

 by a helix or spirally coiled thread of feebly staining 

 substance. Arranged on this snail-shell-like thread 

 are a number of chromatin bars, which may appear 

 to be of different thicknesses owing to the fact that 

 they are situated at different depths. These bars do 

 not extend quite across the organism, which is thus 

 really unsegmented, though at first sight it may 

 present a " chambered " appearance. During periods 

 of great activity of the spirochaete for example, divi- 

 sion the nucleus undergoes much change, which 

 will be described later. 



There are two methods of multiplication by simple 

 division of spirochaetes, and both can be observed in 

 life. The organisms divide both longitudinally and 

 transversely, the first method resulting in long, 

 narrow forms, the second in shorter, thick ones. 

 Preceding longitudinal division, there are nuclear 

 changes, best seen in large spirochaetes such as 

 Spirochata balbianii of the oyster and Tapes, and 

 S. anodonta. The bars of chromatin begin to con- 

 centrate their substance into two masses, one 

 at either end. The two portions gradually draw 

 apart, and two rows of dots are seen instead of bars. 

 Meanwhile the basal granule at the origin of the 

 membrane divides into two, and following that, the 

 membrane splits longitudinally, so that the spiro- 

 chaete now shows two membranes and two basal 

 granules on one body, while the chromatin extends 



